Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Assets:
Available for sale securities	$ 18,080	[1]	$ 15,207	[1]
Trading securities	246		207
Residential mortgage loans held for sale	89		76
Fair value, recurring
Assets:
Available for sale securities	17,234	[2]	14,363	[2]
Trading securities	246		207
Residential mortgage loans held for sale	1,298		2,856
Residential mortgage loans	89	[3]	76	[3]
Derivative assets	1,586		1,972
Total assets	20,453		19,474
Liabilities:
Derivative liabilities	807		915
Short positions	19		10
Total liabilities	826		925
Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	973		1,507
Liabilities:
Derivative liabilities	476		617
Foreign Exchange Contract | Fair value, recurring
Assets:
Derivative assets	237		201
Liabilities:
Derivative liabilities	214		183
Equity Contract | Fair value, recurring
Assets:
Derivative assets	293		177
Liabilities:
Derivative liabilities	35		33
Commodity Contract | Fair value, recurring
Assets:
Derivative assets	83		87
Liabilities:
Derivative liabilities	82		82
US Treasury and Government | Fair value, recurring
Assets:
Available for sale securities	26		41
Trading securities	1		1
US Government Agencies Debt Securities | Fair value, recurring
Assets:
Available for sale securities	1,653		1,911
Trading securities	20		6
US States and Political Subdivisions Debt Securities | Fair value, recurring
Assets:
Available for sale securities	205		212
Trading securities	21		17
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises | Fair value, recurring
Assets:
Available for sale securities	11,353		8,730
Trading securities	1		7
Other Debt Securities | Fair value, recurring
Assets:
Available for sale securities	3,839		3,277
Trading securities	9		15
Other Debt And Equity Securities [Member] | Fair value, recurring
Assets:
Available for sale securities	158	[2]	192	[2]
Trading securities	194		161
Fair Value, Inputs, Level 1 | Fair value, recurring
Assets:
Available for sale securities	118	[2],[4]	120	[2],[4]
Trading securities	195	[4]	162	[4]
Derivative assets	21	[4]	2	[4]
Total assets	334	[4]	284	[4]
Liabilities:
Derivative liabilities	58	[4]	14	[4]
Short positions	17	[4]	8	[4]
Total liabilities	75	[4]	22	[4]
Fair Value, Inputs, Level 1 | Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	12	[4]	2	[4]
Liabilities:
Derivative liabilities	44	[4]	14	[4]
Fair Value, Inputs, Level 1 | Commodity Contract | Fair value, recurring
Assets:
Derivative assets	9	[4]
Liabilities:
Derivative liabilities	14	[4]
Fair Value, Inputs, Level 1 | US Treasury and Government | Fair value, recurring
Assets:
Available for sale securities	26	[4]	41	[4]
Trading securities	1	[4]	1	[4]
Fair Value, Inputs, Level 1 | Other Debt And Equity Securities [Member] | Fair value, recurring
Assets:
Available for sale securities	92	[2],[4]	79	[2],[4]
Trading securities	194	[4]	161	[4]
Fair Value, Inputs, Level 2 | Fair value, recurring
Assets:
Available for sale securities	17,116	[2],[4]	14,243	[2],[4]
Trading securities	50	[4]	44	[4]
Residential mortgage loans held for sale	1,298	[4]	2,856	[4]
Derivative assets	1,247	[4]	1,733	[4]
Total assets	19,711	[4]	18,876	[4]
Liabilities:
Derivative liabilities	710	[4]	865	[4]
Short positions	2	[4]	2	[4]
Total liabilities	712	[4]	867	[4]
Fair Value, Inputs, Level 2 | Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	936	[4]	1,445	[4]
Liabilities:
Derivative liabilities	428	[4]	600	[4]
Fair Value, Inputs, Level 2 | Foreign Exchange Contract | Fair value, recurring
Assets:
Derivative assets	237	[4]	201	[4]
Liabilities:
Derivative liabilities	214	[4]	183	[4]
Fair Value, Inputs, Level 2 | Commodity Contract | Fair value, recurring
Assets:
Derivative assets	74	[4]	87	[4]
Liabilities:
Derivative liabilities	68	[4]	82	[4]
Fair Value, Inputs, Level 2 | US Government Agencies Debt Securities | Fair value, recurring
Assets:
Available for sale securities	1,653	[4]	1,911	[4]
Trading securities	20	[4]	6	[4]
Fair Value, Inputs, Level 2 | US States and Political Subdivisions Debt Securities | Fair value, recurring
Assets:
Available for sale securities	205	[4]	212	[4]
Trading securities	20	[4]	16	[4]
Fair Value, Inputs, Level 2 | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises | Fair value, recurring
Assets:
Available for sale securities	11,353	[4]	8,730	[4]
Trading securities	1	[4]	7	[4]
Fair Value, Inputs, Level 2 | Other Debt Securities | Fair value, recurring
Assets:
Available for sale securities	3,839	[4]	3,277	[4]
Trading securities	9	[4]	15	[4]
Fair Value, Inputs, Level 2 | Other Debt And Equity Securities [Member] | Fair value, recurring
Assets:
Available for sale securities	66	[2],[4]	113	[2],[4]
Fair Value, Inputs, Level 3 | Fair value, recurring
Assets:
Trading securities	1		1
Residential mortgage loans	89	[3]	76	[3]
Derivative assets	318		237
Total assets	408		314
Liabilities:
Derivative liabilities	39		36
Total liabilities	39		36
Fair Value, Inputs, Level 3 | Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	25		60
Liabilities:
Derivative liabilities	4		3
Fair Value, Inputs, Level 3 | Equity Contract | Fair value, recurring
Assets:
Derivative assets	293		177
Liabilities:
Derivative liabilities	35		33
Fair Value, Inputs, Level 3 | US States and Political Subdivisions Debt Securities | Fair value, recurring
Assets:
Trading securities	$ 1		$ 1

[1] Amortized cost of $17,665 and $14,571 at September 30, 2013 and December 31, 2012, respectively.

[2] Excludes FHLB and FRB restricted stock totaling $497 and $349, respectively, at September 30, 2013 and $497 and $347, respectively, at December 31, 2012.

[3] Includes residential mortgage loans originated as held for sale and subsequently transferred to held for investment.

[4] During the three and nine months ended September 30, 2013 and for the year ended December 31, 2012, no assets or liabilities were transferred between Level 1 and Level 2.